Is there a way to bind another function like limit() to pymongo query based on condition?

问题

I have a query which is as below:

def get_data(self, limit=None):
    # I just want to add limit() in case it is set, not otherwise
    self.collection.find(condition)

self.collection refers to the collection in the class. If limit parameter is set I need to bind limit() pymongo function to the query.

NB: the limit is just a sample case it could be any function like sort, etc. So I just want to know is there a mechanism to bind params like this?

回答1:

Do you mean like this?:

def get_data(self, limit=None):
    cursor = self.collection.find(condition)
    if limit is not None:
        return cursor.limit(limit)
    else:
        return cursor

回答2:

below 2 queries return same results

self.collection.find()
self.collection.find().sort([("$natural", pymongo.ASCENDING)])

Sort Natural Order

and also below 2 queries return same results

self.collection.find()
self.collection.find().limit(0)

A limit of 0 is equivalent to no limit. source

so you can combine these and write a single line query as follows

self.collection.find().limit(self.limit or 0).sort(self.sort or [("$natural", pymongo.ASCENDING)])

If you have set values for limit/sort they will be applied otherwise will be ignored.

来源：https://stackoverflow.com/questions/46788207/is-there-a-way-to-bind-another-function-like-limit-to-pymongo-query-based-on-c